The El Mers Group is a geological group in the Middle Atlas of Morocco. It is subdivided into three formations named the El Mers I, II, and III Formations, respectively. It is a marine deposit primarily consisting of marl, with gypsum present in the upper part of unit 3. It is the lateral equivalent of the terrestrial Guettioua Sandstone. Dinosaur remains are among the fossils that have been recovered from the group, most notably those of sauropods and the unusual thyreophoransAdratiklit, Thyreosaurus, and Spicomellus.
The El Mers formations are composed primarily of marls with intermittent layers of limestone and sandstone, characterized by abundant organic matter and benthic fauna.[1] It is delineated into five distinct members, each exhibiting diverse lithological characteristics. The three members comprise a combination of layers of marls, sandstones, and limestones, marked by various unique fossils and organic materials. Sedimentary discontinuities reveal deltaic sequences that exhibit varying sedimentary structures and lithological compositions, reflecting dynamic depositional environments ranging from subtidal to continental. The facies associations within the El Mers Formation are organized into elementary and mesosequences, delineating the transition from prodelta to deltaic plain environments. These sequences capture the evolution of tidal regimes and depositional dynamics.[2]
The shifts in facies and microfauna evolution in our study area reveal intriguing patterns, from the establishment of initial supratidal environments characterized by charophytic marls and ostracod limestones followed by a resurgence of marine conditions, evident from the reappearance of coastal facies and the diversification of ostracod faunas, indicating a significant transgressive phase during the Upper Bathonian–Lower Callovian period. While in the Central High Atlas marine influences ceased by the Upper Bajocian–Lower Bathonian giving way to continental red layers, in the Middle Atlas marine influences persisted until the Upper Bathonian–Lower Callovian boundary, indicating a diachronic filling of the Atlas gulfs towards the Tethyan domain from west to east.[3]
A freshwater ostracod of the family Limnocytheridae. Local members of the genus genus would not be confined to limnic environments, but would be euryhaline or brackish, since they disappear when faunal diversity is at its maximum.
Isolated teeth, cranial and postcranial material, both isolated and semi-articulated
A marine crocodylomorph of the family Teleosauridae. The referral to the genus Steneosaurus should be taken with caution, as this genus was overlumped.
Isolated teeth of unidentified or undescribed/studied theropods. Teeth associated with the Teleosaur "Megalosaurus"mersensis have recently been suggesting to come from indeterminate Averostrans. Other remains need revision.[11][12]
Sauropod tracks of uncertain affinity. There are both small and enormous sauropod tracks, including some among the largest known worldwide, with a pes track length of up to 130 cm.[8]
NHMUK PV R37366 (A dorsal vertebra), three cervical vertebrae (NHMUK PV R37367; R37368), a dorsal vertebra (NHMUK PV R37365), and a left humerus (NHMUK PV R37007)
HIIUC-BN00, a partial postcranial skeleton that includes nine dorsal vertebrae and 21 dorsal rib remains, a limb bone (fibula?), and six dermal elements
A dacentrurine stegosaur with unusual recumbent osteoderms
^Läng, E. (2008). "Les Cétiosaures (Dinosaura, sauropoda) et les sauropodes du Jurassique moyen: revision systématique, nouvelles découvertes et implications phylogénétiques". (Doctoral dissertation, Paris, Muséum national d'histoire naturelle): 1–223. S2CID160327994.
^Zafaty, O.; Oukassou, M.; Riguetti, F.; Company, J.; Bendrioua, S.; Tabuce, R.; Charrière, A.; Pereda-Suberbiola, X. (2024). "A new stegosaurian dinosaur (Ornithischia: Thyreophora) with a remarkable dermal armour from the Middle Jurassic of North Africa". Gondwana Research. 131 (In press): 344–362. Bibcode:2024GondR.131..344Z. doi:10.1016/j.gr.2024.03.009.
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